There are a number of circumstances where a test cell may be required to determine a specific operating characteristic of a fuel or other electrochemical cell--which may have gas diffusion electrodes or solid electrodes. The cells for which the present invention is particularly intended may be generally defined or characterized as being those which require a flow of reactant fluids (either gases or liquids) and liquid electrolyte, into and away from the vicinity of the electrodes, where the an electrolyte is present on the opposite side of the electrodes to that where the reactant fluids are introduced at each electrode. Fuel cells are the type of technology to which the present test cell structure is particularly directed.
Obviously, in any such electrochemical system, there are a number of variables which may be tested for, either in a laboratory situation or in quality assurance testing in a manufacturing situation. For example, the simple teaching and demonstration of fuel cell technology may require that the demonstrator may wish to show the effect of changing one or another of the various components of the test cell--for example, changing the electrolyte or the normality of the electrolyte, changing the reactant fluids, changing the electrodes exposed to the electrolyte and the reactant fluids, and so on. Obviously, in order for any such circumstances to occur, the cell structure being utilized must be capable of being easily assembled and dis-assembled.
Still other circumstances occur which require the use of a test cell structure which is capable of easy assembly and dis-assembly. Often, in research or laboratory circumstances, and relating generally to electrochemical research, it may be important to vary the use of differing components of a system under controlled conditions. Electrodes for use in batteries, fuel cells, electrosynthesis, electrodialysis, and other related fields, require an easy way of substituting one electrode structure for another in an otherwise controlled environment. The evaluation of electrochemical processes which are being developed in a laboratory, or the components required for such processes, require a controlled environment; and for the validity of empirical results to be considered, a test cell structure and environment should be provided in which only a single component or a controlled group of components is changed at any one time.
Still further, in the manufacture of components for use in commercial fuel cells and the like--those which may be used in hospitals, laboratories, military installations, etc.--there is the requirement for quality assurance of the various components being manufactured. Thus, for example, components having known characteristics, such as electrolytes and reaction gases, may be used to test the operating characteristics of sample electrodes. A known electrochemical couple between the gases, in the presence of a known electrolyte, may be calculated to develop a specific voltage having specific current density in an electrode sample of given thickness and surface area. By being capable of mounting an electrode sample, for example, in a frame having a given exposed area, quality assurance of the material of the electrode sample may be easily tested for.
All of the above very often require that the test cell be capable of operating in a wide range of temperatures, and moreover that the test cell be transparent at least in the reaction regions thereof so as to observe the electrochemical processes as they are carried out within the cell. Of course, given that the reaction gases on the one hand, and more particularly the electrolytes, may be highly alkaline or acidic, it is important to assure a liquid-tight sealing relationship within the test cell so as to protect the scientists working in the environment thereof, and indeed so as to protect the laboratory desks, etc. on which the test cells may be placed.
Still further, it may be required that long term testing of an electrochemical system be conducted where the temperature of the electrolyte is closely controlled. In those circumstances, it is appropriate to provide a well as an electrolyte reservoir, and to provide suitable means for controlling the circulation of the electrolyte into the electrolyte chamber of the test cell, while at the same time controlling and maintaining the temperature of the electrolyte at a predetermined value. All of these considerations are met by a test cell according to the present invention, by the simple expedient of providing a well into which a heat exchanger may be placed, and by providing electrolyte circulation means--usually a gas lift pump--to ensure appropriate electrolyte circulation at a controlled rate.
Thus, the present invention provides for a test cell structure for fuel cell technology and the like, which is capable of easy assembly and dis-assembly, and which assures fluid-tight sealing relationship between the electrolyte chamber and the reactant fluid chambers on each side of electrodes placed at the sides of the electrolyte chamber.
This present invention further provides a test cell structure having an electrolyte reservoir and an electrolyte circulation system whereby the operating temperature and the flow rate of the electrolyte may be closely controlled.
Still further, this invention provides for a test cell structure having differing mounting frames for electrodes, where in all cases the mounting frames provide the fluid-tight sealing relationship of the body of the test cell where the electrolyte chamber is located, to the blocks mounted at each side thereof--in which blocks are the reactant fluid chambers of the electrochemical system.
Several prior commercial structures have been available in the market. For example, a test cell for diffusion electrodes from Prototech Corporation, Model PTC, has been provided. However, that test cell is expensive, it requires dis-assembly of a minimum of eight fastening means for the simple replacement of an electrode, it does not provide for easy replacement of electrolyte, neither does it provide an easy means for making electrical connections to the cell to determine the electrochemical system operating characteristics. Still further, the Prototech device permits only the mounting of large-scale electrode structures (in the order of 3 inches square), which is itself fraught with danger when the electrode structures being tested are of a highly frangible or otherwise fragile nature.
The present invention, on the other hand, provides a mounting frame for the electrodes, which may be easily replaced by assembly and dis-assembly of only the respective reactant fluid chamber away from the body of the cell; and in the usual embodiment that assembly and dis-assembly is effected by fastening or unfastening not more than four threaded fastening bolts or other devices. Moreover, the present invention provides a frame having a reasonable electrode area, large enough for meaningful empirical results, but small enough that highly frangible or otherwise fragile electrode structures can be handled. In a usual embodiment, the exposed electrode area within the electrode mounting frames is 2.5 square cm.
Another device which is available in the market is manufactured by ElectroCell AB of Sweden. Most of the shortcomings of the Prototech device are present in the ElectroCell device, including especially high price and large electrode areas.
A precursor, more crudely constructed test cell structure, has been described in a paper given in May, 1986, before a meeting of the Electrochemical Society and published in the proceedings thereof, by Dr. K. Tomantschger (one of the inventors herein) and others, all of a predecesor laboratory institute to Astris Inc., the assignee of the present invention.
As noted above, the present invention generally comprises two embodiments: the first embodiment incorporates a simple electrolyte reservoir within the body of the test cell, relying primarily on convective flow within the electrolyte to promote circulation of the electrolyte to and from the electrolyte chamber; the other embodiment incorporates a well associated with the body, having a pumping arrangement for electrolyte circulation, and being such as to accommodate temperature control of the electrolyte.